1. Field of the Invention
The present invention relates to an apparatus and method for operating an idle mode in a wireless communication system. More particularly, the present invention relates to an apparatus and method for changing a paging cycle while operating an idle mode of a Mobile Station (MS) for effective resource management and reduced power consumption.
2. Description of the Related Art
In broadband wireless communication systems, an idle mode is provided to reduce power consumption in a Mobile Station (MS) and also to effectively manage resources used in a Base Station (BS).
In an idle mode, monitoring is only periodically performed on a broadcast channel when the MS is not registered to a specific BS. The idle mode is operated when transmitted and received traffic of the MS is not generated for more than a predetermined time duration. That is, when in the idle mode, actions required to operate a normal mode (e.g., periodic ranging, channel monitoring, reporting, and handover) are not performed. Instead, an active state is maintained in which the monitoring is performed only in a predetermined interval. Therefore, power consumption can be reduced and the BS can more effectively use resources. In order to manage MSs, after entering the idle mode, the MSs are grouped such that the MSs existing within the same paging zone are included in one group.
FIG. 1 illustrates a method of operating an idle mode in a conventional wireless communication system. Referring to FIG. 1, an MS 100 transmits a De-REGistration REQuest (DREG-REQ) message to a BS 102 in step 110. The BS 102 transmits a De-REGistration CoMmanD (DREG-CMD) message to the MS 100 in step 112. Thereafter, the MS 100 enters the idle mode in step 114.
After entering the idle mode, the MS 100 operates the idle mode by using a paging cycle 116. The paging cycle 116 is determined by transmitting and receiving the DREG-REQ message and the DREG-CMD message. The paging cycle 116 includes a paging interval 118 and a paging unavailable interval 120. The paging interval 118 represents a time duration during which the MS 100 is synchronized with the BS 102 in the downlink and decodes a broadcast paging message. The paging unavailable interval 120 represents a time duration during which the MS 100 performs a power-down operation and consequently, a downlink service is not ensured.
In the idle mode, the paging unavailable interval 120 should be short in order for the MS 100 to rapidly respond to traffic. However, the paging unavailable interval 120 should be long in order to increase power efficiency. Therefore, when the idle mode is operated according to a fixed paging cycle provided in the conventional wireless communication system, it is difficult to obtain both the power savings and the rapid response to the traffic.
The conventional wireless communication system provides a method of changing a paging cycle to achieve the power savings of the MS or the rapid response to the traffic. In this method, inconveniently, the MS in the idle mode transitions to a normal mode, and thereafter, re-enters the idle mode by re-transmitting and receiving the DREG-REQ and the DREG-CMD messages.
In addition, the method of changing the paging cycle, after allowing the MS to transition from the idle to the normal mode, is ineffective in terms of resource utilization of the BS when the number of available MSs is limited.